1 Gregor Mendel

Mendelian Inheritance 2 Gregor Mendel Austrian monk  Studied science and mathematics at University of Vienna  Conducted breeding experiments with the garden pea Pisum sativum  Carefully gathered and documented mathematical data from his experiments Formulated fundamental laws of heredity in early 1860s  Had no knowledge of cells or chromosomes  Did not have a microscope

3 Fruit and Flower of the Garden Pea

4 Garden Pea Traits Studied by Mendel

Mendelian Inheritance 5 Blending Inheritance Theories of inheritance in Mendel’s time:  Based on blending  Parents of contrasting appearance produce offspring of intermediate appearance Mendel’s findings were in contrast with this  He formulated the particulate theory of inheritance  Inheritance involves reshuffling of genes from generation to generation

6 Mendel’s Monohybrid Crosses: An Example

Mendelian Inheritance 7 One-Trait Inheritance Mendel performed cross-breeding experiments  Used “true-breeding” (homozygous) plants  Chose varieties that differed in only one trait (monohybrid cross)  Performed reciprocal crosses ­Parental generation = P ­First filial generation offspring = F 1 ­Second filial generation offspring = F 2  Formulated the Law of Segregation

Mendelian Inheritance 8 Mendel’s Monohybrid Crosses: An Example

Mendelian Inheritance 9 Law of Segregation Each individual has a pair of factors (alleles) for each trait The factors (alleles) segregate (separate) during gamete (sperm & egg) formation Each gamete contains only one factor (allele) from each pair Fertilization gives the offspring two factors for each trait

Mendelian Inheritance 10 Modern Genetics View Each trait in a pea plant is controlled by two alleles (alternate forms of a gene) Dominant allele (capital letter) masks the expression of the recessive allele (lower- case) Alleles occur on a homologous pair of chromosomes at a particular gene locus  Homozygous = identical alleles  Heterozygous = different alleles

11 Homologous Chromosomes

Mendelian Inheritance 12 Genotype Versus Phenotype Genotype  Refers to the two alleles an individual has for a specific trait  If identical, genotype is homozygous  If different, genotype is heterozygous Phenotype  Refers to the physical appearance of the individual

Mendelian Inheritance 13 Punnett Square Table listing all possible genotypes resulting from a cross  All possible sperm genotypes are lined up on one side  All possible egg genotypes are lined up on the other side  Every possible zygote genotypes are placed within the squares

14 Punnett Square Showing Earlobe Inheritance Patterns

15 Try this one MONOHYBRID CROSS Cross a heterozygous tall plant with a heterozygous tall plant (use T = tall and t = short) Determine expected genotype and phenotype ratios.

16 Try these! Show work 1.Cross a heterozygous red flower with a white flower. What is the genotype and phenotype ratio for the offspring? Key: R = red r = white

Mendelian Inheritance 17 Two-Trait Inheritance Dihybrid cross uses true-breeding plants differing in two traits  Observed phenotypes among F 2 plants  Formulated Law of Independent Assortment ­The pair of factors for one trait segregate independently of the factors for other traits ­All possible combinations of factors can occur in the gametes

Mendelian Inheritance 18 Try Mendel’s Classic Dihybrid Cross Cross two heterozygous tall, heterozygous green pod producing plants. Use a punnett square to show expected offspring and complete a phenotype ratio. Key: T = tallG = green pods t = shortg = yellow pods

19 Two-Trait (Dihybrid) Cross

20 Must Know Your Vocab!Homozygous?Heterozygous?Genotype?Phenotype?

21 Try this one – DIHYBRID CROSS 2 traits Key: T = tallR = red ­ ­ t = shortr = white ­ ­Cross two heterozygous tall, heterozygous red flowered plants. ­ ­What is the phenotypic ratio of the offspring?

22 Two-Trait (Dihybrid) Cross

23 P-square practice Practice crosses – on a separate sheet of paper. Show parental crossShow parental cross Show p-squareShow p-square Show phenotype ratioShow phenotype ratio

24 WHAT’s IN YOUR GENES? Mom = 22 autosomes plus X sex chromosome Dad = 22 autosomes plus X or Y chromosome

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26 Boy or Girl? Dad determines this – sperm carries 22 autosomes and either an X or Y sex chromosome BOYS – your mom gave you the X and dad gave you the Y – so what?

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29 Sex-linked – disorders carried on the X chromosome -Colorblindness -Hemophilia -Baldness (?)

30 Analyze Sex-linked traits Due tom!

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33 - Albinism ppt - Albinism ppt -Huntingtons ppt -Final concepts

34 Autosomal Recessive Pedigree Chart

35 Autosomal Dominant Pedigree Chart

36 INHERITING A GENE - ALBINISM

37 This is an albino skunk. The cells are not able to produce the protein that causes color.

38 Cells in the skin produce a black- brown pigment called melanin.

39 The chemical melanin is produced by specialized cells in the epidermis called melanocytes.

40 The melanin leaves the melanocytes and enters other cells closer to the surface of the skin.

41 Different shades of skin colors is determined by the amount of melanin deposited in these epidermal cells

42 Sunlight causes melanocytes to increase production of melanin.

43 A tan fades because the cells break down the melanin.

44 Some organisms, such as the octopus, can rapidly change from light to dark.

45 They control the color by scattering the melanin in the cell for a dark color, and concentrating the melanin in the center for light color.

46 Melanin is made by the melanocytes by chemically changing the amino acid, phenylalanin, into tyrosine and then into melanin.

47 An enzyme is required to change tyrosine into melanin.

48 If the enzyme is not present, then melanin cannot be produced by the melanocytes.

49 The result of no melanin is an albino.

50 The eyes of an albino appear pink because there is no dark melanin in the eye to absorb light.

51 The blood in the retina and iris reflects red light, resulting in pink eyes.

52 The gene that produces this enzyme is on chromo- some 9

53 If both the genes produce the enzyme tyrosinase, there is plenty to convert tyrosine to melanin.

54 If neither gene produces tryosinase, no melanin is produced and…

55 The crow is an albino rather than the normal black

56 What if one gene is normal and one gene does not produce the enzyme?

57 The one normal gene produces enough enzyme to make normal crow color

58 This albino squirrel received one albino gene from the father and one albino gene from the mother.

59 But what if a squirrel gets a normal gene from one parent and an albino gene from the other parent?

60 The one functioning gene produces enough enzyme to make melanin for normal coloration.

61 Is it possible for two normal colored cockatiels to have an albino offspring?

62 Yes! Remember the albino has two genes for albinism. One gene from the father and one gene from the mother.

63 To be albino, both genes must be albino genes

64 A normal colored bird could have one albino gene and one normal gene.

65 If the sperm of a normal colored male pigeon has an albino gene and the ova it fertilizes has an albino gene than the offspring will be albino.

66 The same happens in humans. A normal pigment father and mother can have an albino offspring.

67 We can see this in a genetic “family tree” called a pedigree. The circles are females, the squares are males. The open symbols are normal coloration, the black symbols are albino.

68 The parents in the circle have normal pigment.

69 Most of the offspring received at least one normal gene from a parent.

70 But one female offspring received an albino gene from both the mother and the father.

71 A Punnett square is a matrix to show the genetics of a mating.

72 What is the probability of an albino doe giving birth to a “normal” fawn if she has mated with a “normal” male?

73 The female must have two albino genes (use small “a” for the albino gene - aa

74 Since the albino gene is relatively rare, the male probably has two normal genes of color. (Capital “A” stands for the normal gene) - AA

75 AA X aa

76 Next, add the possible sperm and ova genes. A A a a Aa

77 As long as there is one normal gene, none of the offsprings will be albino A A a aa a Aa

78 Therefore, all offsprings will have a normal and an albino gene. A A a aa a Aa

79 An albino must get one albino gene from the father and one albino gene from the mother.

80 Then how could an albino female penguin have an albino chick.

81 The “normal” colored father must have one “normal coloration gene and one albino gene.

82 There is only one way for two normal colored parents to produce an albino offspring.

83 Both parents must have one normal gene and one albino gene.

84 Aa X Aa Both parents have one gene for normal and one gene for albinism.

85 Aa X Aa A a The father’s sperm is 50% with normal gene and 50% with albino gene.

86 Aa X Aa A a 50% of the mother’s ova have a normal gene and 50% of the ova have the albino gene A a

87 Aa X Aa A a A a AA aaAa The ova and sperm may combine to form an offspring with two normal genes, a normal gene and an albino gene, or two albino genes.

88 Aa X Aa A a A a AA aaAa Only the offspring with two albino genes will lack pigment.

89 Sometimes an albino is born and there is no history of albinism in the colony.

90 The color gene in the cell that produced this white flower changed to an albino gene.

91 A change in a gene is called a mutation.

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